Rheostat



B. M. LEECE Dec. 12, 1944.

RHEOSTAT Filed Deo. 11, 1941 N mw R. wl|ll |Ihh|| [IMM SQW. d. w A MN s QN 1 w Hummm M HHHHH BY @v/Z577' M 565 Paten-ted Dec. 12, 1944 RHEOSTAT Bennett M. Leece, Shaker Heights, Ohio, asslgnor to The Lecce-Neville Company, Ohio, a corporation of Ohio Cleveland,

Application Deeember 11, 1941, serial Ne. 422,539

(ci. eci-4s) 9 Claims.

This invention relates generally to voltage reglulators for use with various types of electrical generating apparatus including the generators which supply current to the auxiliary equipment on aircraft and other motor vehicles. More particularly, the invention relates to a novel rheostat for use in such voltage regulators and for other purposes.

Voltage regulators of the electromagnetic type have been used heretofore with the generators of aircraft and other motor vehicles and many of such devices have operated on the principle of intermittently connecting a resistance of iixed value into, and disconnecting the same from, 4the generator eld circuit by the'use of cooperating contacts which are rapidly opened and closed by a vibratory armature. During recent times, however, the number of electrically operated auxiliary devices used on aircraft and other motor vehicles have been extensively increased and the generators have likewise been increased in size or rating to supply the necessary power to such auxiliaries. In attempting to apply the electromagnetic vibratory-contact type of regulator having a field resistance of xed value to such generators of increased size, I have found that due to the relatively large current variations in the eld circuit, the vibratory contacts of the regulator have frequently been subjected to destructive burning as the result oi sparking occurring at this point. The present invention provides an improved rheostatfor use in such voltage regulators and which enables such regulators to operate more eciently and satisfactorily with generators of higher rating and substantially eliminates such sparking and burning.

An object of my invention is to provide an improved lconstruction for a rheostat of the kind having a rocking contact member.

Another object of this invention is to provide an improved rheostat of the kind mentioned in which novel means is employed for retaining the rocking contact in proper cooperation with the stationary contact member.

The invention may be further briefly sum marized as consisting in .certain novel combinations and arrangements of parts hereinafter described and particularly set out in the appended claims.

In the accompanying sheet of drawings:

Fig. 1 is a plan view of a rheostat constructed according to my invention;

Fig. 2 is a partial perspective View showing the /means for retaining the rocking Contact member in position; and

tail. Before proceeding with the detailed description, however, I wish it; to be understood that the invention is not to be considered as limited to the particular rheostat illustrated and described, but should be regarded as embracing various other similar devices coming within the scope of the appended claims.

As shown in Figs. l and 3, my improved rheostat is embodied in a voltage regulator having a base HJ which forms a mount or support for a relay H and a field resistance i2. The relay i l may comprise a substantially L-shaped frame i3 of magnetizable material and a magnet i4 mounted on an arm i3d of such frame with its core i 5 extending substantially parallel to the arm 93h of the frame. The core I5 carries coils or windings it and il which will be described hereinaiter.- The relay ll also includes an armature l pivotally connected with the frame by the pivot pin i9, and a pair of cooperating contact members 20 and 2| which control the auxiliary circuits of the generator 22 and the energization of the coils i6 and Il.

The armature i8 may be in the form of a bell crank lever having one arm portion which eX- tends across the core l5 and another arm portion which extends generally parallel with the arm portion 53h of the frame and may have a tension spring 23 connected therewith. The tension of the spring 23 may be varied as desired by means of the adjusting screw 24. v

The contact member 26, which in this instance is shown as the stationary contact member, comprises a row of individual contact elements or segments 25 separated from each other by intervening insulating pieces Zii. The segments 25 and the insulating pieces 26 may be arranged in a row or pile and may be held together by means of a clamping screw 2l extending therethrough and which is suitably insulated from the segments. The contact member 28 may also include a backing plate 28 which is spaced from, or otherwise insulated from, the segments 25 and has its ends connected to a pair of end blocks 29a and 2912 formed of insulating material and in which the head and nut of the clamping screw 2l may be recessed. The contact member 2li may be suitably mounted on the base i0 so as to extend transversely of the outer end of the armature it and in substantially parallel relation to the resistor I2. 'Ihe individual segments 25 are connected with the resistor I2 at spaced points therealong by a plurality of taps 30. may be connected with one end of the resistor I2 by the tap 30a and the last segment of the row may be connected with the other end of the resistor by the tap 30h.

The movable contact member 2| is in the form of a curved metallic bar or rocker which has rocking engagement with the row of segments 25 of the stationary contact member 20. The curvature of the contact member 2| is preferably such that it will engage at least two of the segments 25 at one time as its point of engagement with the contact member 20, and this point of contact will travel back and forth along the Contact member 23 as rocking movement is imparted to the contact member 2| by the armature I3.

As shown in the drawing, the contact member 2| is connected with the outer end of the armature I8, and while this may be accomplished in various ways, I show in this instance a forked portion or U-shaped member 3| which is suitable connected to the curved contact member substantially at the midpoint of the latter as by means of solder or the screw 32. The U-shaped member 3l thus forms a substantially rigid proiecting arm or lever portion on the back of the curved contact member 2| by which this contact member can be rocked on the segments 25.

An anti-friction bearing 33 mounted on the outer end of the armature engages in the recess of the U-shaped member 3i and provides a freely movable operating connection between the armature and the curved contact member 2|. With the arrangement `lust described, it will be seen that when the magnet I4 is sufficiently deenergized, the armature I8 is shifted away from the magnet core I by the spring 23 and the contact member 2l will be rocked toward the left, as seen in Figs. l and 3, and the point of engagement with the contact member 20 will shift toward the end contact element 25a. Likewise, when the energization of the magnet I4 is increased sufciently and the armature I8 is drawn toward the magnet core, the contact member 2l will be rocked in the opposite direction and the point of contact will travel toward the end segment 25E.

To prevent the contact member 2| from sliding or walking on the contact member 2t, I provide a retaining means which may be in the form of an elongated :dat spring 35 having one end thereof connected to an end of the contact member 2|, as indicated at 3S, and its opposite end anchored to the other or remote end of the contact member 2t, as by means of the screws 31 connecting the same to the insulating block 29h. The spring 35 is constructed with a rectangular opening 3B therein of a size and shape to permit the contact member 2i to extend through the spring for cooperation with the segments of the contact member 2D. The spring 35 thus holds the contact member 2| against creeping or shifting in any'direction relative to the Contact member 20 and yet permits the contact member 2| to have the desired rocking contact with the row of segments 25.

In addition to the retaining spring 35, I may provide means for pressing the contact member 2| against the Contact member 2-so that good electrical contact will be obtained therebetween.

The first or initial segment 25a of the row f This pressure means may comprise tension springs 39 which are anchored on the contact member adjacent the ends'thereof by being connected to ears 28a provided on the backing plate 28 and are connected with extension pieces 2|a provided at the end of the contact member 2|.

In Fig. 3 I show my rheostat being used in connection with voltage regulation and embodied in an electrical system containing a generator 22. The various circuit connections can be best described by referring to the wiring diagram shown in Fig. 3. As shown in this diagram, the generator 22 has a shunt field winding 40 which has one end connected with the brush 4| and its other end connected with the rocking contact member 2| by the conductor 42. The winding I6 of the regulator is a voltage coil having one end connected with the brush 43 of the generator by the conductor 44 and its other end connected with the brush 4| of the generator by the conductor 45. The winding I1 is a bucking coil, that is, a coil which magnetically opposes the coil I6. One end of this coil is connected with the brush 43 of the generator by the conductor i4 and its other end is connected with the brush il by a circuit extending through the conductor #i5 to the point 45a and then through aportion of the eld circuit and the shunt field winding 40.

In the field circuit the brush 43 of the generator is connected with one end of the resistor I2 through a portion of the conductor 44 and through the conductors 41 and 48. The point 45a, with which one end of the bucking coil I1 of the relay is connected by the conductor 46,

is connected with an intermediate tap or point |20, of the resistor I2 by means of the short conductor 49. A resistance 5D of suitable value connects the conductor 41 with the point 45a and extends in parallel circuit relation with the conductor 48 and an adjacent end section |2b of the resistor I2. An external circuit or load may be connected with the terminals of the generator through the pair of load conductors 5|.

When the generator 22 is about to be started up, the magnet I4 of the regulator is substantially deenergized and the armature is held away from the core I5 by the spring 23, and the point of contact between the contact member 2| and the stationary contact member 20 will be at the end segment a. With the contact member 2| in this position, it will be seen that none of the resistance provided by the resistor I2 will be ineluded in the field circuit, and hence the generator will receive full rleld excitation during the starting thereof. The field circuit at this time will extend from the brush 43, through a portion of the conductor d4, through conductors 41 and 48, through tap connection a, to end segment 25a, and then through contact member 2|, conductor 42, and through the field Winding 4U, back to the brush 4| of the generator.

As the speed of the generator increases, its terminal voltage will build up, thus increasing the energization of the winding I6 of the regulator magnet I4. This will cause the armature I8 to be drawn toward the core l5, and the resulting rocking of the contact member 2| will cause the point of contact with the member 20 to travel toward the right along the segments 25 a distance corresponding with the section of the resistor I2 which is needed in the field circuit to hold the terminal voltage substantially constant. At this time, the field current will be divided and ascuas the two portions will iiow` respectively through the resistance section |2b. and the parallel resistor 50.

Ii the speed oi'. the generator 22 decreases, the energization of magnet winding IB likewise decreases and permits the spring 23 to rock the contact member 2| toward the left, thereby decreasing the length of the section of the resistor I2 which is contained in the eld circuit. During the operation of the generator 22, the contact member 2| will be rocked back and forth on the segmental contact member 20 in accordance with changes in the speed of the generator, and when the contact member 2| has been moved a distance suiilcient to compensate for the change, it will remain relatively stationary to hold the terminal voltage of the generator at the desired value until another change in generator speed occurs. The contact member 2| will also be rocked in a similar manner on the segmental contact member 20 whenever the load on the generator changes sufliciently to alter the speed or terminal voltage. l

During the operation of the generator the contact member 2| has appreciable rocking movement on the contact member 20 only when changes occur in the speed or load of the generator, lbut it may have a small amount of vibratory movement either continuously or from time to time which may be only sufficient to shift the point of engagement to one or the other of a pair of adjacent segments 25. This relatively small vibratory movement of the contact member 2i will be suflicient to compensate for slight variations and will maintain the terminal voltage substantially constant.

As mentioned above, the magnet winding il is a bucking coil which magnetically'opposes the coil i6. The purpose of the winding il is to render the 'regulator more accurately responsive to changes in the load or speed of the generator and more effective in compensating for such changes. I have observed that the .hysteresis effect, occurring in the frame and armature of the relay as changes in magnetization take place, tends to produce an undesirable variable action in the regulator because the hysteresis effect is different when the speed of the generator is increasing from what it is when the speed of the generator is decreasing. I have found that this undesirable action of the regulator resulting from the hysteresis eiect in the magnet frame and armature can be largely overcome or com-pensated by the use of the bucking coil i.

As pointed out above, one end of the bucking coil il is connected with the brush 43 of the generator by the conductor 44 and its other end is connected with the intermediate point 92d of the resistor by the conductors B6 and 49. From this intermediate point of the resistor, the return circuit for the winding Il is coextensive with the portion of the eld circuit which extends through the contact members 20 and 2|, the conductor 42, and the eld winding 60, to the brush 4|.

During the operation of the regulator, the energization of the bucking coil Il, and hence its eiectiveness as a regulating force or factor, will vary as the point of engagement of the contact member 2| shifts along the contact member 2li. In general, the energization of the bucking coil increases when the speed or load of the generator decreases and decreases when the speed or load of the generator increases. In the present form of my apparatus as shown in the drawing, the bucking coil will be oi' maximum effectiveness when the contact member 2| is on segment 25o of the contact member 20 which is connected with the point |2a of the resistor l2 because at this time the resistance oi the bucking coil circuit is a minimum. As the contact member 2| shifts toward the right from the segment 25h, the effectiveness of the bucking coil decreases and when the contact member 2| shifts toward the left from the segment 25h, the effectiveness of the bucking coil increases.

It is important to observe that in the operation of my regulator, the contact member 2i always maintains electrical contact with the contact, member 2d and there is no opening and closing of the field and regulator circuits at this point as has been the case heretofore with regulators of the vibratory type. Since these circuits are always maintained at the contact members 2U and 2|, there will be little likelihood of the contact members being burned or pitted as the result of sparking at this point,

While I have illustrated and described my improved regulating apparatus and rheostat in a more or less detailed manner, it will be understood, of course, that I do not wish to be limited to the particular details and arrangements herein described, but regard my invention as including such changes and modifications as do not constitute a departure from the spirit of the invention and the scope of the appended claims.

Having thus described my invention', I claim:

l. In a rheostat, a member comprising a series of spaced contacts, a resistor having taps connected with said contacts, a curved contact member rockable on said spaced contacts, a flexible retaining strip overlying said contacts and having one end attached to one end of said curved contact member, and its other end anchored to the opposite end of the first-mentioned member, said strip permitting such rocking of said curved contact member lbut resisting longitudinal shifting of the latter relative to saidV contacts and having an opening therein exposing the contacts for engagement by said curved contact member, and means for imparting rocking movement tc said curved contact member.

2. In a rheostat, a member comprising a series of spaced contacts, a resistor having taps conn nected with said contacts, a curved contact memberv rockable on said spaced contacts, a flexible retaining strip overlying said contacts and having one end attached to one end of said curved contact member and its other end anchored to the opposite end of the first-mentioned. member, said strip permitting such rocking of said curved contact member but resisting longitudinal shifting of the latter relative to said contacts and having an opening therein exposing the contacts for engagement by said curved Contact member,

a pair of tension springs connected with the ends of said curved contact member for drawing the same against said contacts, and means for iinengaging the ends of said curved member and acting to` hold the same against said ilrst-mentioned member.

4. In a rheostat, a member having a series of contact segments insulated from each other, a resistor having taps connected with the respective segments, a rocker-shaped contact element rockably engaging said segments, and,a ilexible retaining strip connected with one end of the rstmenti'oned member and with the other end oi' said rocker-shaped element, said strip permitting such rocking engagement by said rocker-shaped element but resisting longitudinal shifting of said rocker-shaped element relative to said series of segments.

5. In a rheostat, a member having a series of contact segments insulated from each other, a resistor having taps connected with the respective segments, a rocker-shaped contact element rockably engaging said segments, and a flexible retaining strip connected with one end of the rst-mentioned member and with the other end of said rocker-shaped element so as to permit such rocking engagement by said rocker-shaped element but resisting longitudinal shifting of said rocker-shaped element'I relative to said series of segments, said strip having an opening therein exposing said segments for engagement by said rocker-shaped element.

6. In a rheostat, a member having a series of contacts insulated from each other, a curved Contact member rockable on said series of contacts, a flexible strip connecting said curved member with the first-mentioned member, and a pair of springs engaging the ends of said curved member and acting to hold the same against said first-mentioned member, said strip permitting such rocking of said curved member but resisting longitudinal shifting of said curved member relative to said series of contacts and having an opening therein exposing said contacts for engagement by said curved member.

7. A rheostat comprising a member having a series of Contact segments insulated from each. other, a curved contact member rockably engaging the nrst member, a resistor having taps conf nected with said segments, a flexible retaining strip having one end thereof connected with one end of the nrst member and its other end connected with the opposite end of said curved member, said strip permitting such rocking of said curved member but resisting longitudinal shifting of said curved member relative to said seriesA oisegments, a magnet having a coil and a movable armature, and means connecting said armature with said curved member for actuating the latter.

8. A rheostat comprising a member having a series of contact segments insulated from each other, a. curved contactl member rockably engaging the first; member, a. resistor having taps connected with said segments, a flexible retaining strip having one end thereof connected with one end of the iirst member and its other end connected with the opposite end oi' said curved member, said strip permitting such rocking of said curved member but resisting longitudinal shifting of said curved member relative to said series of segments, a magnet having a coil and a movable armature, a forked portion on the concave side of said curved member adjacent the midpoint thereof, and an antifriction bearing in said forked portion and connecting said curved member with said armature.

9. In a rheostat, a resistor having a row of contact elements, a curved contact member, a pair of tension springs engaging the ends of said curved member and holding the same in rocking engagement with said contact elements, a flexible retaining strip connected with said curved meinn ther and having an opening exposing said elements for engagement by said curved member, said strip permitting such rocking of said curved member but resisting longitudinal shifting of said curved member relative to said row of contact elements, a magnet having a coil and a movable armature, a forked portion on the concave side of said curved member adjacent the midpoint thereof, and an antiriction bearing in said forked portion and connecting said curved member with said armature.

BENNETT M. LEECE. 

